Spool valve

ABSTRACT

Two stage spool valves having, in a single assembly, a first stage spool and a second stage spool. The first stage spool may have a solenoid actuator with a return spring, with the second stage spool having either a hydraulic return or a spring return, or both. The solenoid actuator may be comprised of a stationary structure defining a magnetic flux path, including a stationary structure pole face, that together with a moveable structure, including a moveable structure pole face, define a substantially zero air gap magnetic circuit when the solenoid actuator is actuated, the pole faces of the stationary structure and the moveable structure each being defined in part by soft magnetic iron and in part by hardened steel, the hardened steel of the moveable structure contacting the hardened steel of the stationary structure and the soft magnetic iron of the moveable structure being face to face with the soft magnetic iron of the stationary structure when the solenoid actuator is actuated.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 60/771,112 filed Feb. 7, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of solenoid actuated spoolvalves.

2. Prior Art

Solenoid actuated spool valves are well known in the prior art. Suchvalves include single solenoid spring return valves and double solenoidvalves, either of which may or may not incorporate magnetic latching. Anexample of such valves may be found in U.S. Pat. No. 5,640,987. Alsoknown are two-stage spool valve systems, the first stage being asolenoid valve that hydraulically controls a second stage spool valve.See for instance U.S. Pat. No. 6,739,293.

In certain applications, such as in fuel injectors and hydraulic valveactuation systems, solenoid actuated spool valves must have a usefullife of billions of cycles. This requires that the wear of the variousparts be held to a minimum, in turn requiring hardened steels, such asby way of example, 52100 or 440C. These materials, however, have arelatively low magnetic field saturation density in comparison to thesaturation density of physically soft magnetic steels (iron), such asannealed 1020. These steels may have a saturation density of as much astwice the saturation density of the hardened steels, and since magneticforces are proportional to the square of the flux density, may provideapproximately four times the maximum actuation force provided by thehardened steels for the same pole area.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section of a preferred embodiment of the presentinvention in the unactuated state.

FIG. 2 is a cross section of the preferred embodiment of the two stagevalve of FIG. 1 in the partially actuated state.

FIG. 3 is a cross section of the preferred embodiment of the two stagevalve of FIG. 1 in the fully actuated state.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First referring to FIG. 1, a cross-section of one embodiment of thepresent invention may be seen. This embodiment is a two-stage spoolvalve, the first stage being electromagnetically or solenoid actuatedand the second stage being hydraulically actuated by the first stage.The first stage includes the combination of hardened steels for improvedwear characteristics, and soft magnetic irons, for improved magneticcharacteristics. The first stage also uses a single solenoid coil with aspring return, the spring return comprising two springs, one active overthe entire return stroke and one active only over approximately one-halfof the return stroke, to effectively provide a stepped spring returnforce of some fraction of the solenoid actuation force to provide fastaction both on actuation and on return. The second stage uses ahydraulic return with the actuation of the first stage providing ahydraulic actuating force greater than the hydraulic return force, bothforces being dependent on the pressure of a control fluid being suppliedby a source of fluid under pressure.

As may be seen in FIG. 1, a body member 20 forms the body or housing fora pilot spool 22, as well as a second stage spool 24. At one end of thebody member 20 is a solenoid coil 26, a pole piece 28 and a cover 29.Between the pole piece 28 and the body member 20 is an insert 30. Alsoon an extension 34 of the pilot spool 22 is another insert 32.Preferably insert 30 is press fitted into the pole piece 28 and insert32 is press fitted onto an extension 34 on the pilot spool 22. Ingeneral, inserts 30 and 32 are fabricated of a high saturation densitymaterial such as annealed 1020 or high saturation density ironsspecifically intended for use in magnetically actuated devices. Also ingeneral, the other parts of the two-stage valve shown in FIG. 1 arepreferably hardened steel parts which, while having some magneticcharacteristics, are chosen primarily for their wear resistance, such as52100 or 440C. In that regard, insert 30 is assembled into pole piece 28and insert 32 is assembled onto extension 34 of the pilot spool 22before the end faces thereof are finished so that in the finished parts,the face of insert 30 is coplanar with the face of pole piece 28 and theface of insert 32 is coplanar with the face of the extension 34.

FIG. 1 represents the unactuated condition of the two-stage spool valve.In this condition, port 36, connected to a source S of fluid underpressure, is blocked by the land on the pilot spool 22. Any leakage intogroove 38 in the body member 20 is coupled through passage 40 to thecenter region 42 of the pilot spool 22, and from there, into springregion 44 to the vent V port 46. Consequently, region 48 behind pushpins 50 will be unpressurized. However, port 50, also coupled to sourceS of fluid under pressure, is coupled to region 52 behind push pins 54.This pressure forces the second stage spool 24 to its right-mostposition as shown in FIG. 1. At the same time, spring 56 pushes pushmember 58 to the left, forcing the pilot spool 22 to the left until theleft end thereof abuts the corresponding face of the second stage spool24. If desired, a separate stop could be provided for the leftmostmotion of the pilot spool 22.

In the preferred embodiment, there are three push pins 50 and only twopush pins 54, with all push pins being of the same diameter.Consequently, with push pins 54 being pressurized and push pins 50 notbeing pressurized, the assembly will seek the position shown in FIG. 1.However, when an actuating current is applied to the solenoid coil 26,the pilot spool 22, with the insert 32 thereon, will be magneticallyattracted toward the right, initially being resisted only by spring 56until push member 58 abuts member 62, as shown in FIG. 2. In thepreferred embodiment this occurs at approximately the mid position ofthe pilot spool 22 where the source S of fluid under pressure coupled toport 36 begins to be coupled to region 48 behind push pins 50. With theair gap in the magnetic circuit being smaller than in FIG. 1, the totalmagnetic force on the pilot spool 22 will have typically increased. Atthe same time, further motion of the pilot spool 22 causes spring 60 toalso start to compress as a result of push member 58 engaging member 62and moving the same to the right against the force of spring 60. This,in essence, provides a step in the spring force, better approaching thetypical shape of the magnetic force versus pilot spool position. Thisprovides fast actuation, while also providing a boost force ondeactivation to assure a fast return to the unactuated position.

Finally, when the solenoid actuator is fully actuated as illustrated inFIG. 3, both springs 56 and 60, both of which were initially preloaded,have been further compressed, with the face of extension 34 on the pilotspool 22 and insert 32 resting against the adjacent face of pole piece28 and insert 30. In this position, fluid is coupled from the source Sthrough port 36 and annular passage 38 to the region 48 behind push pins50, hydraulically forcing push pins 50 to the left. As stated before, inthe preferred embodiment, push pins 50 and 54 are of the same diameter,though the second stage spool 24 only has two push pins 54, whereas thepilot spool 22 has three push pins 50. Accordingly, when region 48behind push pins 50 is pressurized, the force pushing second stage spool24 to the left is greater than the force encouraging second stage spool24 to the right. In that regard, note that as the pressure of the sourceS of fluid under pressure increases, the actuating forces and returnforces on the second stage spool 24 similarly increase. Also in thatregard, spring 70, operative between end cap 72 and second stage spool24, determines the position of the second stage spool when the pressureof the source S is not present, such as will occur when the pump orother fluid pressurizing means is off. In particular, that positionwould be the position shown in FIG. 1, wherein the second stage spool 24couples the control port C 68 to vent port V 46, whereas when thesolenoid is actuated as in FIG. 3, the source S of fluid under pressurein port 50 is coupled to control port C 68, with flow between controlport C 68 and vent port V 46 being blocked. Thus the two-stage valve ofthis embodiment is a two-stage three-way valve coupling a control portto a source of fluid under pressure or to a vent, depending on the stateof actuation of the solenoid actuator in the pilot valve.

As previously described, inserts 30 and 32 are high saturation densitymagnetic materials, chosen not primarily for their wear characteristics,but for their high saturation density. Wear on these materials isminimized by the fact that when the two-stage valve is actuated, thehardened extension 34 on the pilot spool 22 is stopped by portion 70 onthe hardened steel pole piece 28. The high saturation density inserts 30and 32, however, concentrate the flux to provide a high flux densitybetween the two members in the actuated state of FIG. 3, providing botha high attraction force during actuation as well as a high holding forceafter actuation, provided the cross-section of the hardened steelmembers, such as pole piece 28 and body member 20, have sufficientcross-section to not saturate even at their lower saturation densities.Thus inserts 30 and 32, having approximately twice the saturationdensity of pole piece 28 and body member 20, allow the concentration ofthe same flux over approximately one-half the area. Since the magneticforce of attraction between inserts 30 and 32 is proportional to thesquare of the flux divided by the area, the use of inserts 30 and 32 mayat least approximately double the actuation force of the solenoidactuator, allowing stronger springs for springs 56 and 60, therebyincreasing both the actuation speed and the release speed of thetwo-stage valve. In that regard, the advantage of using a two-stagevalve in many applications is the fact that larger flow porting betweena control port and the source and vent ports may be obtained while stillusing a relatively small, low power solenoid actuator for the pilotspool. Also it should be noted that magnetic latching of the pilot spoolin the actuated position can be used, if desired, primarily as a resultof selection of the force of springs 56 and 60 and/or the presence orabsence of a holding current in the solenoid coil 26. In that regard, ifmagnetic latching is not used, a full actuation current may bemaintained in the solenoid coil 28 throughout each actuation period, ora full current pulse may be used for actuation purposes, followed by asubstantially reduced holding current, which will maintain substantiallythe full magnetic field strength in the magnetic circuit because of thefact that, on actuation, the air gap in the magnetic circuit goes to asubstantially zero gap. Also, while the present invention has beendisclosed with respect to a three-way, two-stage valve, it will beobvious to those skilled in the art that simple changes may be made toprovide some other type of valve, such as by way of example, a two-stagetwo-way valve.

In the illustrations presented herein, the assembly or manner of holdingtogether of end cap 72, body member 20, pole piece 28 and cover 29 isnot shown. The various parts may be joined in any manner, such as isknown in the art, such as by way of example, by screws, by threadedparts, by placement in and closure of an outer housing, or by assemblyand entrapment in the housing or body of a higher assembly.

The present invention as described herein has been described withrespect to various unique features thereof. It is to be understood,however, that various subcombinations of the features described may alsobe advantageously incorporated in single or two-stage valves. Thus whilecertain embodiments of the present invention have been disclosed anddescribed herein, it is to be understood that various changes in formand detail may be made therein without departing from the spirit andscope of the invention.

1. A two stage spool valve comprising: in a single assembly; a firststage spool moveable between first and second positions, the firstposition coupling a source of fluid under pressure to a first hydraulicarea associated with a second stage spool that is moveable between thirdand fourth positions, and the second position coupling the firsthydraulic area to a vent; the first hydraulic area being disposed sothat fluid under pressure acting against the first hydraulic areaencourages the second stage spool to the third position; the secondstage spool having a return disposed to encourage the second stage spoolto the fourth position; the second stage spool being configured tocouple a first port to a second port when in one of the third and fourthpositions and to not couple the first port to the second port when inthe other of the third and fourth positions; a solenoid actuatordisposed to move the first stage spool to one of the first and secondpositions when actuated, and a return spring disposed to encourage thefirst stage spool to the other of the first and second position; thesolenoid actuator being comprised of a movable structure and astationary structure, the stationary structure defining a magnetic fluxpath, including a stationary structure pole face, that together with themoveable structure, including a moveable structure pole face, define asubstantially zero air gap magnetic circuit when the solenoid actuatoris actuated, the pole faces of the stationary structure and the moveablestructure each being defined in part by soft magnetic iron and in partby hardened steel, the hardened steel of the moveable structurecontacting the hardened steel of the stationary structure and the softmagnetic iron of the moveable structure being face to face with the softmagnetic iron of the stationary structure when the solenoid actuator isactuated.
 2. The two stage spool valve of claim 1 wherein the part ofthe magnetic path defined only by hardened steel has a larger crosssectional area than the part of the face to face area of the softmagnetic iron part of the pole faces when the solenoid is actuated toaccommodate the lower saturation density of hardened steel in comparisonwith soft magnetic iron.
 3. The two stage spool valve of claim 1 whereinthe return of the second stage spool is a hydraulic return.
 4. The twostage spool valve of claim 1 wherein the return of the second stagespool is a spring return.
 5. The two stage spool valve of claim 1wherein the return of the second stage spool is both a hydraulic returnand a spring return.
 6. The two stage spool valve of claim 1 wherein thereturn spring for the first stage spool is comprised a combination oftwo springs, a first spring being active to encourage the first stagespool away from an actuated position to the opposite position throughoutthe first stage spool's motion between the first and the secondpositions, a second spring being active to encourage the first stagespool away from the actuated position toward the opposite positionthroughout approximately only one half first stage spool's motion fromthe actuated position toward the opposite position.
 7. The two stagespool valve of claim 1 wherein the second stage spool couples the firstport to a third port when in the other of the third and fourthpositions.
 8. The two stage spool valve of claim 1 wherein the secondstage spool has a second hydraulic area coupled to a source of fluidunder pressure and disposed to encourage the second stage spool to thefourth position; the first hydraulic area being larger than the secondhydraulic area.
 9. The two stage spool valve of claim 8 wherein thefirst and second hydraulic areas are defined by cross sectional areas ofa plurality of pins.
 10. The two stage spool valve of claim 1 whereinthe first stage spool and the second stage spool are coaxial.
 11. A twostage spool valve comprising: in a single assembly; a first stage spoolmoveable between first and second positions, the first position couplinga source of fluid under pressure to a first hydraulic area associatedwith a second stage spool that is moveable between third and fourthpositions, and the second position coupling the first hydraulic area toa vent; the first hydraulic area being disposed so that fluid underpressure acting against the first hydraulic area encourages the secondstage spool to the third position; the second stage spool having asecond hydraulic area coupled to a source of fluid under pressure anddisposed to encourage the second stage spool to the fourth position; thefirst hydraulic area being larger than the second hydraulic area; thesecond stage spool being configured to couple a first port to a secondport when in one of the third and fourth positions and to not couple thefirst port to the second port when in the other of the third and fourthpositions.
 12. The two stage spool valve of claim 11 wherein the secondstage spool couples the first port to a third port when in the other ofthe third and fourth positions.
 13. The two stage spool valve of claim11 further comprising a first return spring configured to encourage thesecond stage spool toward the fourth position.
 14. The two stage spoolvalve of claim 11 further comprised of a solenoid actuator disposed tomove the first stage spool to one of the first and second positions whenactuated, and a return spring disposed to encourage the first stagespool to the other of the first and second positions.
 15. The two stagespool valve of claim 14 wherein the solenoid actuator is comprised of amovable structure and a stationary structure, the stationary structuredefining a magnetic flux path, including a stationary structure poleface, that together with the moveable structure, including a moveablestructure pole face, define a substantially zero air gap magneticcircuit when the solenoid actuator is actuated, the pole faces of thestationary structure and the moveable structure each being defined inpart by soft magnetic iron and in part by hardened steel, the hardenedsteel of the moveable structure contacting the hardened steel of thestationary structure and the soft magnetic iron of the moveablestructure being face to face with the soft magnetic iron of thestationary structure when the solenoid actuator is actuated.
 16. The twostage spool valve of claim 15 wherein a part of the magnetic pathdefined only by hardened steel has a larger cross sectional area thanthe part of the face to face area of the soft magnetic iron part of thepole faces when the solenoid is actuated to accommodate the lowersaturation density of hardened steel in comparison with soft magneticiron.
 17. The two stage spool valve of claim 16 wherein the returnspring for the first valve is comprised a combination of two springs, afirst spring being active to encourage the first stage spool away froman actuated position to the opposite position throughout the first stagespool's motion between the first and the second positions, a secondspring being active to encourage the first stage spool away from theactuated position toward the opposite position throughout approximatelyonly one half first stage spool's motion from the actuated positiontoward the opposite position.
 18. The two stage spool valve of claim 11wherein the first stage spool and the second stage spool are coaxial.19. The two stage spool valve of claim 11 wherein the first and secondhydraulic areas are defined by cross sectional areas of a plurality ofpins.
 20. A two stage spool valve comprising: in a single assembly; afirst stage spool moveable between first and second positions, the firstposition coupling a source of fluid under pressure to a first hydraulicarea associated with a second stage spool that is moveable between thirdand fourth positions, and the second position coupling the firsthydraulic area to a vent; the first hydraulic area being disposed sothat fluid under pressure acting against the first hydraulic areaencourages the second stage spool to the third position; the secondstage spool having a return spring disposed to encourage the secondstage spool to the fourth position; the second stage spool beingconfigured to couple a first port to a second port when in one of thethird and fourth positions and to not couple the first port to thesecond port when in the other of the third and fourth positions; asolenoid actuator disposed to move the first stage spool to one of thefirst and second positions when actuated, and a return spring disposedto encourage the first stage. spool to the other of the first and secondpositions.
 21. The two stage spool valve of claim 20 wherein thesolenoid actuator is comprised of a movable structure and a stationarystructure, the stationary structure defining a magnetic flux path,including a stationary structure pole face, that together with themoveable structure, including a moveable structure pole face, define asubstantially zero air gap magnetic circuit when the solenoid actuatoris actuated, the pole faces of the stationary structure and the moveablestructure each being defined in part by soft magnetic iron and in partby hardened steel, the hardened steel of the moveable structurecontacting the hardened steel of the stationary structure and the softmagnetic iron of the moveable structure being face to face with the softmagnetic iron of the stationary structure when the solenoid actuator isactuated.
 22. The two stage spool valve of claim 21 wherein the part ofthe magnetic path defined only by hardened steel has a larger crosssectional area than the part of the face to face area of the softmagnetic iron part of the pole faces when the solenoid is actuated toaccommodate the lower saturation density of hardened steel in comparisonwith soft magnetic iron.
 23. The two stage spool valve of claim 22wherein the return spring for the first stage spool is comprised acombination of two springs, a first spring being active to encourage thefirst stage spool away from an actuated position to the oppositeposition throughout the first stage spool's motion between the first andthe second positions, a second spring being active to encourage thefirst stage spool away from the actuated position toward the oppositeposition throughout approximately only one half first stage spool'smotion from the actuated position toward the opposite position.
 24. Thetwo stage spool valve of claim 23 wherein the second stage spool couplesthe first port to a third port when in the other of the third and fourthpositions.
 25. The two stage spool valve of claim 23 wherein the secondstage spool has a second hydraulic area coupled to a source of fluidunder pressure and disposed to encourage the second stage spool to thefourth position; the first hydraulic area being larger than the secondhydraulic area.
 26. The two stage spool valve of claim 25 wherein thefirst and second hydraulic areas are defined by cross sectional areas ofa plurality of pins.
 27. The two stage spool valve of claim 20 whereinthe first stage spool and the second stage spool are coaxial.